It is common in the formation of medical and laboratory filters, such as blood filters or blood filtration housings containing filters, to form filter housings for filter media from one or more sheets of flexible polyvinyl chloride (PVC) material. It is also common to manufacture filter housings from rigid plastics such as acrylic, polypropylene, or a similar material.
Many types of devices are commercially available for separating whole blood components. Some machines are fully automated while others rely on manual operations performed by technicians. On a gross level, blood components include plasma (water and protein), red blood cells, leukocytes, and platelets. Filter media is commercially available to filter leukocytes from blood. A filter pad media for filtering leukocytes from blood cells is disclosed in U.S. Pat. No. 5,591,337, commonly owned by the assignee hereof.
While filter housings manufactured from flexible PVC material offer the benefit of having a flexible housing, it has been heretofore difficult to provide an efficient and reliable method for forming an inlet port and an outlet port in the filter housing. Prior art filter housings made from one or more sheets of PVC material have taught the formation of the port along the peripheral seal of the respective PVC material sheet edges. Typically, a short piece of tubing is used as the port. See, for example, U.S. Pat. No. 4,035,304 to Watanabe issued 12 Jul. 1977 and entitled Blood Filtering Bag. However, it is difficult to form a complete and reliable seal at the junction of the PVC material sheets and the tubing that serves as the port. Both an incomplete seal, as well as a weak seal can lead to fluid leaking from the filter assembly during the filtering process.
Introducing fluid into a filter housing at the seal of its panels or sheets is also less desirable when the flow characteristics of the fluid across the filter media are important (e.g. laminar flow or even flow across the filter media). If the fluid enters the housing immediately adjacent the filter media, the bubble strength of the filter media may be quickly surpassed by increased blockage of the filter media with filtered particulate and the resulting increased pressure within the filter housing may cause the filter media to rupture or burst. This is a very undesirable result in that it is difficult, if not impossible to immediately detect a ruptured filter membrane. Alternatively, increased blockage of the filter media may lead to turbulent fluid flow through the filter assembly. Many fluids react poorly to turbulent flow.
A similar prior art filter is taught in published European Patent Publication No. 0 516 846 to Sakamoto published 9 Dec. 1992 and entitled Bag-Like Filter. This application teaches the formation of filter housings from heat-fusible polyethylene films. In one embodiment the inlet and outlet ports are formed from polyethylene tubing fused between the film and the filter at their edges. Alternatively, separate inlet and outlet ports having a construction similar to a valve placed in a tire tube may be fused through an opening formed in the central regions of the film sheets.
Other prior art devices, such as U.S. Pat. No. 5,507,904, commonly owned by the assignee hereof, teach the formation of the inlet and outlet ports in the wall of a thermoplastic sheet filter housing by first forming a slit in the filter housing wall, inserting a separate tube through the slit and heating the mating materials to fuse the tube and sheet. While providing a very reliable filter assembly, extra care must be taken during the manufacturing process to ensure that the slit is not too large, the tube is properly placed prior to heating, and a good seal is formed around the tubing-wall junction. Some prior art filter assemblies do not include positive stops for the conduits attached to their filter ports. Without a stop, the possibility exists that the rubber or plastic conduit may be inserted too far into the port, thereby possibly damaging or piercing the filter media. In addition, if solvent is used to bond the conduit to the port, the solvent may contact and thereby degrade the filter media.
Filter housings molded from hard plastics such as acrylic allow for the formation of the inlet and outlet ports at almost any location along the wall or panel of the filter housing. The location is primarily limited only by the sophistication of the mold or die. However, the resulting filter assemblies have the drawback that they are not flexible and thus cannot substantially prevent a phenomenon common in fluid filtering processes known as “foaming.” It is also sometimes necessary to centrifuge a blood container having a filter device attached thereto. A hard plastic filter housing may puncture or damage the blood container during the centrifuge process.
Most of the whole blood collected from donors today is not itself stored and used for transfusion. Instead, the whole blood is separated into its clinically proven components (typically red blood cells, platelets, and plasma), which are themselves individually stored and used to treat a multiplicity of specific conditions and diseased states. For example, the red blood cell component is used to treat anemia; the concentrated platelet component is used to control thrombocytopenic bleeding; and the platelet-poor plasma component is used as a volume expander or as a source of Clotting Factor VIII for the treatment of hemophilia.
In the United States, whole blood components collected in a non-sterile, or “open”, system (e.g. one that is open to communication with the atmosphere) must, under governmental regulations, be transfused within twenty-four hours. However, when whole blood components are collected in a sterile, or “closed”, system (e.g., one that is closed to communication with the atmosphere), the red blood cells can be stored up to forty-two days (depending upon the type of anticoagulant and storage medium used); the platelet concentrate can be stored up to five days (depending upon the type of storage container); and the platelet-poor plasma may be frozen and stored for even longer periods. Conventional systems of multiple, interconnected plastic bags have met with widespread acceptance, because these systems can reliably provide the desired sterile, “closed” environment for blood collection and processing, thereby assuring the maximum available storage periods.
In collecting whole blood components for transfusion, it is desirable to minimize the presence of impurities or other materials that may cause undesired side effects in the recipient. For example, because of possible febrile reactions, it is generally considered desirable to transfuse red blood cells substantially free of the white blood cell components, particularly for recipients who undergo frequent transfusions.
One way to remove leukocytes is by washing the red blood cells with saline. This technique is time consuming and inefficient, as it can reduce the number of red blood cells available for transfusion. The washing process also exposes the red blood cells to communication with the atmosphere, and thereby constitutes a “non-sterile” entry into the storage system. Once a non-sterile entry is made in a previously closed system, the system is considered “opened”, and transfusion must occur within twenty-four hours, regardless of the manner in which the blood was collected and processed in the first place. In the United States, an entry into a blood collection system that presents the probability of non-sterility that exceeds one in a million is generally considered to constitute a “non-sterile” entry.
Another way to remove leukocytes is by filtration. Systems and methods for accomplishing this within the context of conventional multiple blood bag configurations are described in Wisdom U.S. Pat. Nos. 4,596,657 and 4,767,541, as well as in Carmen et al U.S. Pat. Nos. 4,810,378 and 4,855,063. In these arrangements, an inline leukocyte filtration device is used. The filtration can thereby be accomplished in a closed system. However, the filtration processes associated with these arrangements require the extra step of wetting the filtration device before use with a red blood cell additive solution or the like. This added step complicates the filtration process and increases the processing time.
Other systems and methods for removing leukocytes in the context of closed, multiple blood bag configurations are described in Stewart U.S. Pat. No. 4,997,577. In these filtration systems and methods, a transfer assembly dedicated solely to the removal of leukocytes is used. The transfer assembly is attached to a primary blood collection container. The transfer assembly has a transfer container and a first fluid path leading to the transfer container that includes an inline device for separating leukocytes from red blood cells. The transfer assembly also has a second fluid path that bypasses the separation device. Using these systems and methods, leukocytes are removed as the red blood cells are conveyed to the transfer container through the first fluid path. The red blood cells, now substantially free of leukocytes, are then conveyed from the transfer container back to the primary collection container for storage through the second fluid path, this time bypassing the separation device.
A need still exists for an improved biological matter filter housing that is flexible and that includes an inlet or an outlet port integrally formed in the housing. A need exists for an improved filter housing capable of trapping air and preventing foaming of the fluid or blood passed through the filter. A need also exists for a form of a fluid filter having an inlet and an outlet formed tangentially in a flexible wall of the filter assembly. A need exits for an improved flexible filter housing having integral ports including positive stops for conduits connected to the filter also exists. Because these types of devices are often used only once (e.g. disposable) a need exists for an efficient, reliable and low cost method of making the filter assembly.